This paper is concerned with theoretical treatment of a thermoelastic buckling problem for a rectangular plate which possesses orthotropic material properties in in-plane direction and inhomogeneous properties in thickness direction. We assume that rectangular plate is subjected to a non-uniform heat supply from both boundary surfaces and has symmetric material properties in thickness direction which is given by power product form of thickness coordinate z. Three dimensional temperature change in a steady state and associated thermoelastic buckling behavior are developed theoretically for an orthotropic inhomogeneous rectangular plate under mechanical boundary condition of simply supported edge. Effects of orthotropy and inhomogeneity in material properties on critical buckling temperature change and post-buckling behavior in a rectangular plate are examined through numerical calculation.